Trimerisation and oligomerisation of olefins using a chromium based catalyst

ABSTRACT

The invention provides a mixed heteroatomic ligand for an oligomerization of olefins catalyst, which ligand includes at least three heteroatoms, of which at least one heteroatom is sulfur and at least two heteroatoms are not the same. The invention also provides a multidentate mixed heteroatomic ligand for an oligomerization of olefins catalyst, which ligand includes at least three heteroatoms of which at least one is a sulfur atom. The ligand may also contain, in addition to sulfur, at least one nitrogen or phosphorous heteroatom.

This application is a divisional application of U.S. patent applicationSer. No. 10/499,225 with a filing date of Jan. 26, 2005, now U.S. Pat.No. 7,300,904, which is a National Stage of International ApplicationNo. PCT/ZA02/00216, filed on Dec. 19, 2002, which claims the benefit ofU.S. Provisional Application No. 60/342,560, filed on Dec. 20, 2001, andSouth African Application Serial No. 2001/10435, filed on Dec. 20, 2001.The contents of all of the foregoing applications are herebyincorporated by reference in their entirety

FIELD OF THE INVENTION

This invention relates to a ligand and a catalyst system, moreparticularly an olefin oligomerisation or trimerisation catalyst system.

BACKGROUND OF THE INVENTION

The oligomerisation of olefins, primarily α-olefins, with chromiumcatalysts has been extensively studied. More specifically, a number ofchromium catalysts have been developed and used to trimerise olefins. Inthis regard, the trimerisation of ethylene to 1-hexene is significantsince, in addition to its use as a specific chemical, 1-hexene isextensively used in polymerization processes either as a monomer orco-monomer. Furthermore, the trimeric products derived from longer chainolefins could be well utilized as synthetic lubricants (e.g.polyalphaolefins/PAOs), as well as various other applications such ascomponents of drilling muds, and as feedstock to prepare detergents andplasticizers.

Prior art chromium based ethylene trimerisation processes include:

-   a) A process in which olefins are trimerised by passing the olefin    in contact with a catalyst comprising the reaction product of a    chromium compound, an organoaluminium compound hydrolyzed with a    specific amount of water and a donor ligand selected from    hydrocarbyl isonitriles, amines and ethers (U.S. Pat. No.    4,668,838);-   b) A process to trimerise ethylene to 1-hexene comprising contacting    ethylene with a stabilized catalyst system comprising a chromium    source, a pyrrole-containing compound, a metal alkyl and an aromatic    compound (European Patent No. 0 668 105);-   c) A process for preparing α-olefin oligomers, which comprises    carrying out oligomerisation of an α-olefin in a solvent by reacting    said α-olefin with a chromium-based catalyst system comprising a    combination of at least a chromium compound, an amine or metal    amide, and an alkylaluminium compound, in a contacting mode that the    chromium compound and the alkylaluminium compound are not previously    contacted with each other (U.S. Pat. No. 5,750,817);-   d) A process for oligomerising ethylene to produce 1-butene and/or    1-hexene wherein catalytic composition is obtained by mixing at    least one chromium compound with at least one aryloxy aluminium    compound with general formula R_(n)Al(R′O)_(3−n) where R is a linear    or branched hydrocarbyl radical containing 1 to 30 carbon atoms, R′O    is an aryloxy radical containing 6 to 80 carbon atoms and n is a    whole which can take the values 0,1 or 2, and with at least one    other hydrocarbyl aluminium compound selected from    tris(hydrocarbyl)aluminium compound or chlorinated or brominated    hydrocarbyl aluminium compounds (U.S. Pat. No. 6,031,145); and-   e) A process for the trimerisation of ethylene, said process    comprising reacting ethylene, using a catalyst comprising an    aluminoxane and a polydentate phosphine, arsenic and/or antimony    coordination complex of a chromium salt, such that 1-hexene is    formed (U.S. Pat. No. 5,811,618).

SUMMARY OF THE INVENTION

The invention is now described in general terms with reference to theaccompanying drawings.

In the drawings:

FIG. 1 shows a X-Ray Crystal structure ofCrCl₃(bis-(2-ethylsulfanyl-ethyl)-amine), and

FIG. 2 shows a schematic representation (flow diagram) of one embodimentof a olefin oligomerisation process, in accordance with the invention.

This invention recognizes the need for a catalyst system, whichfacilitates the production of 1-hexene in high selectivity whileavoiding the co-production of significant quantities of polyethylene.However, the catalyst system can also be used for the trimerisation oroligomerisation of other olefins, especially α-olefins.

In this regard, it is known from the prior art (e.g. European Patent No.537609) that chromium catalysts comprising a multidentate aminecoordination complex of a chromium salt and an aluminoxane or analkylaluminium compound are generally not particularly effective attrimerising ethylene selectively. This has also been establishedexperimentally as is demonstrated in Example 1 below.

This invention generally relates to how the need for selectivelyproducing 1-hexene from ethylene can be at least partly satisfied byusing a chromium catalyst system containing a multidentate ligand withat least one amine functionality.

Thus, according to a first aspect of the invention there is provided amixed heteroatomic ligand for the oligomerisation of olefins catalyst,which ligand includes at least three donor heteroatoms, of which atleast one donor heteroatom is sulfur and at least 2 donor heteroatomsare not the same.

The ligand may be a multidentate mixed heteroatomic ligand which,includes at least three donor heteroatoms of which at least one is asulfur atom.

The ligand may include, in addition to sulfur, at least one nitrogen orphosphorous donor heteroatom.

The ligand may be selected such that none of the non-carbon based donorheteroatoms are directly bonded to any of the other non-carbon baseddonor heteroatoms.

By “multidentate mixed heteroatomic” is meant a ligand that containsmore than one non-carbon based donor atoms, of which one donor atom isdifferent from the others and of which all the donor atoms arecoordinated to the transition metal in the catalyst system. Theapplicant has found that it is important for catalyst activity that allthe non-carbon based donor atoms coordinate with the transition metal,and the ligand therefore preferably, but not necessarily, needs at leastone bridging atom between the donor atoms to provide the necessarydistances between the donor atoms and to allow the ligand to assume thenecessary spatial orientation for coordination of all donor atoms. FIG.1 contains the molecular structure of a complex between CrCl₃ and anexample of such a multidentate mixed heteroatomic ligand, namelybis-(2-ethylsulfanyl-ethyl)-amine. Selected bond distances and angles ofthis molecular structure are summarized in Table 1.

TABLE 1 Selected bond distances and angles ofCrCl₃(bis-(2-ethylsulfanyl- ethyl)-amine) Chelate bite angle 83.07(5)°82.90(5)° Cr—S bond distances 2.4508(7) Å 2.4556(7) Å Cr—N bond distance2.1059(18) Å

As can be seen from FIG. 1, this specific multidentate mixedheteroatomic ligand has a meridional arrangement in the complex, therebyenabling the formation of two Cr—S bonds with nearly equal bonddistances (see Table 1). Such a meridional arrangement of the ligand isonly possible if there is at least one bridging atom between the donoratoms. As could be expected, the resulting S—Cr—N chelate bite anglesare also very similar in size.

Therefore a multidentate mixed heteroatomic ligand may also be selectedsuch that none of the non-carbon based donor atoms are directly bondedto any of the other non-carbon based donor atoms.

The multidentate mixed heteroatomic ligand may be selected from thefollowing ligand types:

-   a) R¹A(R²BR³)(R⁴CR⁵) wherein R¹, R³ and R⁵ may be hydrogen or    independently be selected from the groups consisting of alkyl, aryl,    aryloxy, halogen, nitro, alkoxycarbonyl, carbonyloxy, alkoxy,    aminocarbonyl, carbonylamino, dialkylamino, or derivatives thereof,    or aryl substituted with any of these substituents; R² and R⁴ may be    the same or different and are C₁ to about C₁₅ hydrocarbyls; A is    nitrogen or phosphorous; and B and C are sulfur or selenium; and-   b) R¹A(R²BR³R⁴)(R⁵CR⁶) wherein R¹, R³, R⁴, and R⁶ may be hydrogen or    independently be selected from the groups consisting of alkyl, aryl,    aryloxy, halogen, nitro, alkoxycarbonyl, carbonyloxy, alkoxy,    aminocarbonyl, carbonylamino, dialkylamino, or derivatives thereof,    or aryl substituted with any of these substituents; R² and R⁵ may be    the same or different and are C₁ to about C₁₅ hydrocarbyls; A and B    are individually nitrogen or phosphorous; and C is sulfur; and-   c) A(R¹BR²R³)(R⁴CR⁵) wherein R², R³, and R⁵ may be hydrogen or    independently be selected from the groups consisting of alkyl, aryl,    aryloxy, halogen, nitro, alkoxycarbonyl, carbonyloxy, alkoxy,    aminocarbonyl, carbonylamino, dialkylamino, or derivatives thereof,    or aryl substituted with any of these substituents; R¹ and R⁴ may be    the same or different and are C₁ to about C₁₅ hydrocarbyls; B is    nitrogen or phosphorous; and A and C are sulfur; and-   d) A(R¹BR²R³)(R⁴CR⁵R⁶) wherein R², R³, R⁵ and R⁶ may be hydrogen or    independently be selected from the groups consisting of alkyl, aryl,    aryloxy, halogen, nitro, alkoxycarbonyl, carbonyloxy, alkoxy,    aminocarbonyl, carbonylamino, dialkylamino, or derivatives thereof,    or aryl substituted with any of these substituents; R¹ and R⁴ may be    the same or different and are C₁ to about C₁₅ hydrocarbyls; B and C    are individually nitrogen or phosphorous; and A is sulfur.

These multidentate mixed heteroatom based ligands can be synthesizedaccording to procedures described in the literature, for example by A.Heβler et al., J. Organomet. Chem., 1998, 533, 39-52, M. Tanaka et al.J. Org. Chem., 2001, 66, 7008-7012, M. Konrad, F. Meyer, K. Heinze, L.Zsolnai. J. Chem. Soc., Dalton Trans., 1998 199-205 and G. Gelbard andP. Rumpf, Bull. Soc. Chem., 1969, 1161-1170.

Specific examples of multidentate mixed heteroatom based ligands mayinclude bis-(2-ethylsulfanyl-ethyl)-amine,bis-(2-methylsulfanyl-ethyl)-amine, bis-(2-butylsulfanyl-ethyl)-amine,bis-(2-decylsulfanyl-ethyl)-amine, bis-(ethylsulfanyl-methyl)-amine,bis-(2-ethylsulfanyl-phenyl)-amine,bis-(2-ethylsulfanyl-ethyl)-phosphine,bis-(2-ethylsulfanyl-ethyl)-ethylphosphine,bis-(2-ethylsulfanyl-ethyl)-phenylphosphine,N-methylbis-(2-ethylsulfanyl-ethyl)-amine,(2-ethylsulfanyl-ethyl)(3-ethylsulfanyl-propyl)-amine,(2-ethylsulfanyl-ethyl)(2-diethylphosphino-ethyl)-amine,(2-ethylsulfanyl-ethyl)(2-diethylphosphino-ethyl)-sulfide,(2-ethylsulfanyl-ethyl)(2-diethylamino-ethyl)-amine,(2-ethylsulfanyl-ethyl)(2-diethylamino-ethyl)-sulfide,(2-ethylsulfanyl-ethyl)(2-diethylphosphino-ethyl)-ethylphosphine,(2-ethylsulfanyl-ethyl)(2-diethylphosphino-ethyl)-phosphine,(2-ethylsulfanyl-ethyl)(2-diethylamino-ethyl)-ethylphosphine,(2-ethylsulfanyl-ethyl)(2-diethylamino-ethyl)-phosphine,bis-(2-diethylphosphino-ethyl)-sulfide,bis-(2-diethylamino-ethyl)-sulfide and(2-diethylphosphino-ethyl)(2-diethylamino-ethyl)-sulfide.

Suitable multidentate mixed heteroatomic ligands arebis-(2-ethylsulfanyl-ethyl)-amine and bis-(2-decylsulfanyl-ethyl)-amineand derivatives thereof. The multidentate mixed heteroatomic ligands canbe modified to be attached to a polymer chain (molecular wt.=1000 orhigher) so that the resulting transition metal complex is soluble atelevated temperatures, but becomes insoluble at 25° C. This approachwould enable the recovery of the complex from the reaction mixture forreuse and has been used for other catalyst as described by D. E.Bergbreiter et al., J. Am. Chem. Soc., 1987, 109, 177-179. In a similarvain these transition metal complexes can also be immobilized bybounding the multidentate mixed heteroatomic ligands to silica, silicagel, polysiloxane or alumina backbone as demonstrated by C. Yuanyin etal., Chinese J. React. Pol., 1992, 1(2), 152-159 for immobilizingplatinum complexes.

According to a further aspect of the invention, there is provided anoligomerisation of olefins catalyst system, which includes a mixedheteroatomic ligand, as described above.

The term “oligomerisation” generally refers to a reaction were all themonomer units of the oligomerisation product are the same. However, itmay also include co-oligomerisation reactions where mixtures of olefinsare used as the reagents thereby yielding products containing more thanone type of monomer unit (i.e. different olefins). Suchco-oligomerisation reactions often yield alkyl- and/or aryl-branchedoligomeric products with distinct properties as demonstrated by C.Pelecchia et al., Macromolecules, 2000, 33, 2807-2814.

The catalyst system may include a transition metal.

The transition metal may be chromium. Molybdenum, tungsten, titanium,nickel, and tantalum may also be used.

The catalyst system may include a combination of a mixed heteroatomiccoordination complex of chromium and an aluminoxane.

The chromium coordination complexes which, upon mixing with analuminoxane, catalyze ethylene trimerisation in accordance with theinvention, may be suitably expressed by the formula LCrX_(n) wherein Xrepresents anions which can be the same or different, n is an integerfrom 0 to 5 and L is a mixed heteroatomic ligand.

The chromium precursor used in the preparation of the coordinationcomplex may be selected from an organic or inorganic chromium compound,with the oxidation state of the chromium atom ranging from 0 to 6.Chromium salts used in the preparation of the chromium coordinationcomplex may be selected from chromium(III) acetylacetonate, chromium(III) acetate, chromium (III) 2,2,6,6-tetramethylheptadionate, chromium(III) tris(2-ethylhexanoate, chromium (III) chloride, chromium (II)acetate, chromium (II) chloride, chromium (III) nitrate and chromium(III) sulphate. Alternatively, organometallic complexes, for example,chromium trichloride tris-tetrahydrofuran complex, (benzene)tricarbonylchromium, chromium hexacarbonyl, and the like, may be used in thepreparation of the chromium coordination complex.

Aluminoxanes for use in the catalyst system can be prepared as known inthe art by reacting water or water containing materials withtrialkylaluminium compounds. Preferred aluminoxanes are prepared fromtrialkylaluminium compounds such as trimethylaluminium,triethylaluminium, tripropylaluminium, tributylaluminium,triisobutylaluminium, thrihexylaluminium or the like, and mixturesthereof. Mixtures of different aluminoxanes may also be used in thecatalyst system. Of these, the more preferred aluminoxane is preparedfrom trimethylaluminium and/or triethylaluminium. The use of saidaluminoxane is necessary to achieve catalytic activity.

The catalyst system may include, in addition to the aluminoxane ormixture of aluminoxanes, also a trialkylaluminium in amounts of between0.01 to 100 mole per mole of aluminoxane. It should however be notedthat aluminoxanes generally also contain considerable quantities of thecorresponding trialkylaluminium compounds used in their preparation. Thepresence of these trialkylaluminium compounds in aluminoxanes can beattributed to their incomplete hydrolysis with water. Any quantity of atrialkylaluminium compound quoted in this disclosure is additional toalkylaluminium compounds contained within the aluminoxanes.

The applicant has found that the trialylaluminium serves as a poisonsscavenger to protect the aluminoxane and in some cases leads to anincrease in the catalytic activity.

The aluminoxane may form part of a mixture of aluminoxanes. Theapplicant has found that at least a portion of the required moreexpensive methylaluminoxane can be replaced with a less expensiveethylaluminoxane, for example, and the resulting mixture shows the same,if not increased, catalytic activity.

The aluminoxane or mixture of aluminoxanes may preferably be selectedfrom methylaluminoxane or ethylaluminoxane.

The chromium coordination complex and the aluminoxane may be combined inproportions to provide Al/Cr molar ratios of from about 1:1 to 10 000:1.

The hydrocarbon conversion catalyst system may be a trimerisation ofα-olefins or trimerisation of ethylene catalyst system.

The hydrocarbon conversion catalyst system described in this inventionmay also be used in combination with another catalyst system suitablefor the polymerization of olefins. In such cases, the oligomerization ortrimerisation products of the catalyst system disclosed in thisinvention could be incorporated into a polymer or other chemical productwith desired properties. This concept of using dual catalyst systems,one for oligomerization and the other for polymerization of olefins, tomanufacture polyethylene copolymers has been demonstrated before forexample by G. C. Bazan, Z. J. A. Komon and X. Bu, J. Am. Chem. Soc.,2000, 122, 1830 and C. Pelecchia et al., Macromolecules, 2000, 33,2807-2814.

The catalyst system may be a trimerisation of α-olefins or trimerisationof ethylene catalyst system.

The multidentate mixed heteroatomic coordination complex of a chromiumsalt may be either added to the reaction mixture, or generated in-situ.Known literature procedures can be used for the ex-situ preparation ofsuch coordination complexes of a chromium salt. Examples of suchprocedures are described by R. D Köhn and G. K. Köhn, Angew. Chem. Int.Ed. Engl., 1994, 33(18), 1877-1878, R. D Köhn et al., Angew. Chem. Int.Ed., 2000, 39(23), 4337-4339 and P. Wasserscheid et al., Adv. Synth.Catal., 2001, 343(8), 814-818.

The catalyst system may include an inert solvent. These inert solventsinclude any saturated aliphatic and unsaturated aliphatic and aromatichydrocarbon and halogenated hydrocarbon. The saturated aliphatic andunsaturated aliphatic hydrocarbon compound can have any number of carbonatoms per molecule, but usually contain less than 20 carbon atoms due tocommercial availability and end use. Preferred solvents include, but arenot limited to, benzene, toluene, xylene, ethylbenzene, mesitylene,heptane, nonane, cyclohexane, methylcyclohexane, 1-hexene,chlorobenzene, anisole and the like.

The individual components of the catalyst system described in thisdisclosure may be combined simultaneously or sequentially in any order,and in the presence or absence of a solvent, in order to give an activecatalyst. The mixing of the catalyst components can be conducted at anytemperature between 0° C. and 150° C. The temperature during the mixingof the catalyst components does not seem to have a significant effect onthe catalyst performance. The presence of an olefin during the mixing ofthe catalyst components generally provides a protective effect which mayresult in improved catalyst performance.

The chromium coordination complex and the aluminoxane are combined inproportions to provide Al/Cr molar ratios of from about 1:1 to 10 000:1,and preferably, from about 1:1 to 1000:1. In this respect, it was foundthat generally significant lower Al/Cr molar ratios are required toachieve an acceptable catalyst performance when the chromiumcoordination complex is completely soluble in the solvent employed forthe oligomerisation reaction.

The catalyst system, or its individual components, may also beimmobilized by supporting it on a heterogeneous surface such as silica,alumina, silica-alumina, MgO, zirconia or the like. This approach wouldalso facilitate the recovery of the catalyst from the reaction mixturefor reuse. The concept was successfully demonstrated with anotherchromium-based ethylene trimerisation catalyst by T. Monoi and Y.Sasaki, J. Mol. Cat. A: Chem., 1987, 109, 177-179. In some cases, theheterogeneous surface (support) can also act as a catalyst component,for example where such supports contain aluminoxane functionalities orwhere the support is capable of performing similar chemical functions asan aluminoxane, which is for instance the case with IOLA™ (a commercialproduct from Davison Catalysts).

It was thus found that the hydrocarbon conversion catalyst systemdescribed in this invention suffered nearly no detectable decrease inits catalytic performance when alumina supported aluminoxane is used,instead of unsupported aluminoxane, during the preparation of thecatalyst system.

According to a further aspect there is provided a process for theoligomerisation of olefins, the process including the step of contactingthe olefins at pressures from atmospheric to 100 barg and attemperatures of from 0° C. to 200° C., with a catalyst system asdescribed above.

The process of this invention may also be carried out in an inertsolvent. Any inert solvent that does not react with trialkylaluminiumand aluminoxane compounds can be used. These inert solvents include anysaturated aliphatic and unsaturated aliphatic and aromatic hydrocarbonand halogenated hydrocarbon. Preferred solvents include, but are notlimited to, benzene, toluene, xylene, heptane, cyclohexane, 1-hexene andthe like. The amount of solvent is not exceptionally critical andgenerally ranges from about 50 to 99.9 wt % of the initial reactionmixture. Nevertheless, since the catalyst productivity tends to besomewhat higher at fairly low catalyst concentrations in the initialreaction mixture (typically in the range of 0.001-0.1 mmol Cr/100 mlreaction mixture), the catalyst concentration is chosen such that thecatalyst productivity and selectivity is maximized.

The catalyst is dissolved in an inert solvent.

The process may include the step of generating the multidentate mixedheteroatomic complex of a chromium salt in-situ in a reaction mixture.

The process of this invention may be carried at pressures fromatmospheric to 100 barg. Generally the process can be performed at anypressure within this range, but here again the actual reaction pressureis chosen such that the catalyst productivity and selectivity ismaximized. Ethylene pressures in the range of 30-60 bar are particularlypreferred.

The process of this invention may be carried out at temperatures from 0°C. to 200° C. The process can normally be conducted at any temperaturewithin this range, but as is the case with the ethylene pressure, theactual reaction temperature is chosen such that the catalystproductivity and selectivity is maximized. Temperatures in the range of80-120° C. are particularly preferred.

The process may be carried out in the presence of an oxidizing agentsuch as oxygen or the like.

The process can normally be conducted at any temperature within thisrange, but as is the case with the ethylene pressure, the actualreaction temperature is chosen such that the catalyst productivity andselectivity is maximized. Temperatures in the range of 80-120° C. areparticularly preferred.

The process may be carried out in the presence of an oxidizing agentsuch as oxygen or the like. In this respect it was found that the use ofolefin reagents, such as ethylene, containing low quantities of oxygen(1-2000 parts per million) resulted in improvements in the performanceof the catalyst system as well as in the product selectivity.

Although the catalyst, its individual components, reagents, solvents andreaction products are generally employed on a once-through basis, any ofthese materials can, and are indeed preferred to, be recycled to someextent in order to minimize production costs.

This process may comprise, in combination a) a reactor, b) at least oneinlet line into this reactor for olefin reactant and the catalystsystem, c) effluent lines from this reactor for oligomerisation reactionproducts, and d) at least one separator to separate the desiredoligomerisation reaction products, wherein the catalyst system mayinclude a multidentate mixed heteroatomic coordination complex of achromium salt and an aluminoxane.

FIG. 2 is a schematic representation (flow diagram) of one embodiment ofthis olefin oligomerisation process using three separators to separatethe reaction products, solvent and spent catalyst (waste). While thisdrawing describes one embodiment of the invention for the purpose ofillustration, the invention is not to be construed as limited by thisschematic flow diagram, but the drawing is rather intended to cover allchanges and modifications within the spirit and scope thereof.

Various additional pumps, valves, heaters, coolers and otherconventional equipment necessary for the practice of this invention willbe familiar to one skilled in the art. These additional equipment havebeen omitted from FIG. 2 for the sake of clarity.

The following description of the flow diagram shown in FIG. 2 providesone method of operating the process, in accordance with the invention,and aims to give a further understanding of the aspects of thisinvention. As used in the description, “reactor effluent” refers to allcomponents that can be removed from an oligomerisation reactor,including, but not limited to, unreacted olefin, catalyst system,oligomerisation product(s) and co-product(s). “Waste” refers to reactionco-product(s) with a higher molecular mass than the desiredoligomerisation reaction product, polymeric products and the usedcatalyst system. “Product” refers to product(s) of the olefinoligomerisation reaction.

Olefin, and optionally oxygen or air, is fed trough inlet line 7/8 intothe oligomerisation reactor 1. Inlet line 5/6 introduces the catalystsystem and optionally, solvent, into the oligomerisation reactor 1.Reactor effluent is removed from reactor 1 via line 9. It should benoted that lines 6, 8 and 9 can be located anywhere on the reactor 1. Itis preferable that the contents in lines 9, 15,16,17 and 19 ismaintained at a higher temperature in order to keep undesirable polymerparticles from precipitating. The formation of such particles may have adetrimental effect on the operation of this process.

Line 9 introduces reactor effluent into separator 2 that separatesunreacted olefin and reaction product(s) from higher boiling solvent(s),reaction product(s) and the used catalyst system. Lines 15/16 is anoptional embodiment of the invention and can be used to facilitate thereturn of the higher boiling compounds in the reactor effluent,including the catalyst system, to reactor 1 via inlet line 6. Line 15/17transports an effluent stream, comprising higher boiling compounds andused catalyst system, from separator 2 to separator 4, which separatesthe solvent from all other compounds in this effluent stream. Line 18 isused to return the solvent to separator 2. Line 19 is an effluent linethat transports waste from separator 4. Line 10 transports effluentcomprising unreacted olefin and the major reaction product(s) fromseparator 2 to separator 3, that separates the unreacted olefin from themajor reaction product(s).

Line 12/14 contains effluent comprising unreacted olefin and smallquantities of very light boiling reaction product(s), e.g. 1-butene, andfacilitates the recovery of the olefinic reagent by transporting it backto inlet line 6. Line 12/14 is a purge line containing unreacted olefinand small quantities of very light boiling reaction product(s) that isused to prevent a build up of very light boiling reaction product(s).Line 11 is an effluent line containing the major reaction product(s).

In another embodiment of the process the reactor and a separator may becombined to facilitate the simultaneous formation of reaction productsand separation of these compounds from the reactor. This processprinciple is commonly known as reactive distillation when the reactionis a homogeneous liquid phase reaction. When the catalyst systemexhibits no solubility in the solvent or reaction products, and is fixedin the reactor so that it does not exit the reactor with the reactorproduct, solvent and unreacted olefin, the process principle is commonlyknown as catalytic distillation.

The oligomerisation process described herein may be used in a process inwhich trimerisation and polymerization of ethylene occur simultaneouslyleading to the incorporation of the trimerisation products into acopolymer. One example of this type of process is described in U.S. Pat.No. 5,786,431.

EXAMPLES OF PERFORMING THE INVENTION

The invention will now be described with reference to the followingexamples which are not in any way intended to limit the scope of theinvention.

In the examples that follow all procedures were carried out under inertconditions, using pre-dried reagents. Chemicals were obtained fromSigma-Aldrich Company unless stated otherwise. All trialkylaluminium andaluminoxane compounds and solutions thereof were obtained from Cromptonand Albemarle Corporation. In all the examples, the molar mass ofmethylaluminoxane (MAO) was taken to be 58.016 g/mol, corresponding tothe (CH₃—Al—O) unit, in order to calculate the molar quantities of MAOused in the preparation of the catalyst systems described in theexamples below. Similarly the molar mass of ethylaluminoxane (EAO) wastaken as 72.042 g/mol, corresponding to the (CH₃CH₂—Al—O) buildingblock. Ethylene oligomerisation reaction products were analyzed by GC-MSand GC-FID.

Example 1 Reaction of CrCl₃(pentamethyldiethylenetriamine)/MAO withEthylene

The reaction was conducted in a 75 mL stainless steel autoclave equippedwith an addition funnel, gas inlet valve and a magnetic stirrer bar. Theaddition funnel was charged with 0.0149 g (0.0449 mmol) ofCrCl₃(pentamethyldietylenetriamine) dissolved in 20 mL of toluene and tothe base of the autoclave was added 9.0 mL of 1.5M MAO solution intoluene. Over 20 minutes the base of the autoclave was heated to 10° C.,after which time the reactor was charged with ethylene to a pressure of40 bar and the addition funnel was opened such that the Cr complexsolution was allowed to mix with the MAO solution. After 30 minutes at aconstant ethylene pressure of 40 bar the reaction was stopped by coolingthe autoclave to 0° C. and releasing excess ethylene. The gas releasedwas collected and analysed by gas-chromatography (GC). The liquidcontained in the autoclave was quenched with ethanol followed by 10%hydrochloric acid, and nonane was added as a GC internal standard. Theliquid/internal standard mixture was also analysed by GC. Both GCanalyses indicated that 0.12 g oligomers were formed of which 0.0048 g(4 mass %) were hexene isomers. Filtration of the liquids gave 0.12 g ofpolyethylene.

Example 2 Preparation of (bis-(2-ethylsulfanyl-ethyl)-amine)

A solution of NaOH (6.0 g, 150 mmol) and ethanethiol (9.3 g, 150.0 mmol)in ethanol (150 ml) was added to a solution of bis(2-chloroethyl)aminehydrochloride (8.8 g, 50.0 mmol) in ethanol (100 ml) at 0° C. Thesolution was stirred for 2 hours at 0° C., then overnight at r.t. Afterfiltering, the filtrate was evaporated to dryness. The residue was takenup in 40-ml diethyl ether and filtered again. After evaporation of thesolvent in vacuo, the product remained as a colourless semisolid. Yield:5.39 g (56%). ¹H-NMR (CDCl₃) δ 1.20 (6H, t, CH₃), 2.52 (1H, s, NH), 2.57(4H, q, SCH₂CH₃), 2.70 (4H, t, SCH₂), 2.83 (4H, t, NCH₂).

Example 3 Preparation of (bis-(2-decylsulfanyl-ethyl)-amine)

A solution of NaOH (3 g, 75 mmol) and decanethiol (15.5 ml, 75 mmol) inethanol (75 ml) was added to a solution of bis(2-chloroethyl)aminehydrochloride (4.4 g, 25 mmol) in ethanol (50 ml) at 0° C. The solutionwas stirred for 2 hours at 0° C. and then for another 16 h at roomtemperature. After filtering, the filtrate was evaporated to dryness.The residue was taken up with dry ether and filtered again. Afterevaporation of the solvent under vacuum, the product remained as acolourless semi-solid. Yield: 9.4 g (90%). ¹H-NMR (CDCl₃) δ 0.87 (6H, t,CH₃), 1.25-1.4 (28H, m, SC₂H₄C₇H₁₄CH₃), 1.56 (4H, qn, SCH₂CH₂C₈H17),1.88 (1H, s, NH), 2.52 (4H, qt, SHCH₂C₉H₁₉), 2.69 (4H, t, SCH₂CH₂NH),2.82 (4H, t, NCH₂).

Example 4 Preparation of CrCl₃(bis-(2-ethylsulfanyl-ethyl)-amine)

A solution of bis[2-(ethylsulfanyl)ethyl]amine (1.06 g, 5.5 mmol) in 20ml THF was added to a solution of 1.87 g (5 mmol) CrCl₃ (THF)₃ in 50 mlTHF at room temperature. The solution turned blue-green immediately andwas stirred for 10 min, after which the solvent was removed in vacuountil about 25 ml remained. A further 50-ml of diethyl ether was added,the solution was filtered and the solid washed, first with a mixture ofdiethyl ether and THF (50 ml each), then with a further 50 ml of diethylether. The solid was dried in vacuo. Yield: 1.28 g (72.6%). Elementalanalysis: Calculated for C₈H₁₉S₂NCl₃Cr (found): C, 27.32 (26.97); H,5.45 (5.99); N, 3.98 (3.64). Crystal data: monoclinic space group P2₁/c,a=7.6255(12), b=13.059(5), c=14.3703(10) Å, β=90.790(11)°, V=1430.9(6)Å³, Z=4, D_(C)=1.633 g·cm⁻³, μ=1.622 mm⁻¹, F(000)=724, 2θ_(max)=54°,4013 reflections, 3126 independent data. Convergence for 138 parametersat wR2=0.0857, R1=0.0351, GOF=1.074 for all data and R1=0.0309 for 2846reflections with />2(/). Residual electron density was 0.439 and −0.549e·Å⁻³. Selected bond distances (Å) and angles (°): Cr—N 2.1059(18),Cr—S1 2.4508(7), Cr—S2 2.4556(7), Cr—Cl1 2.2985(8), CrCl2 2.3184(7),Cr—Cl3 2.3167(7), N—Cr—S1 83.07(5), N—Cr—S2 82.90(5), S1-Cr—Cl197.20(2), S2-Cr—Cl1 96.85(2), N—Cr—Cl1 179.71(5), N—Cr—Cl2 85.82(6) andN—Cr—Cl3 88.64(6).

Example 5 Preparation of CrCl₃(bis-(2-decylsulfanyl-ethyl)-amine)

A solution of 3.93 g (9.4 mmol) of (bis-(2-decylsulfanyl-ethyl)-amine)in 80 ml THF was added to a solution of 3.21 g (8.6 mmol) CrCl₃(THF)₃ in50 ml THF at room temperature. The solution turned blue-greenimmediately and was stirred for 10 min after which all the solvent wasremoved in vacuo. Diethylether (80 ml) was added to the residue and thesolution was cooled overnight in a refrigerator. The solution was thenfiltered and the solid was washed with diethyl ether (3×60 ml). Thesolid was dried in vacuo. Yield: 3.68 g (74.3%). Elemental analysis:Calculated. for C₂₄H₅₁S₂NCl₃Cr (found): C, 50.04 (50.23); H, 8.86(9.19); N, 2.43 (2.16).

Example 6 Ethylene Trimerisation Reaction UsingCrCl₃(bis-(2-ethylsulfanyl-ethyl)-amine)/MAO

CrCl₃(bis-(2-ethylsulfanyl-ethyl)-amine) (0.01407 g, 0.04 mmol) wascombined with 20 ml toluene in a Schlenk vessel and stirred for 5minutes at room temperature. The resulting suspension was thentransferred to a 300 ml pressure reactor (autoclave) containing amixture of toluene (80 ml) and MAO (methylaluminoxane, 27.2 mmol) at 90°C. The pressure reactor was charged with ethylene after which thereactor temperature was maintained at 100° C., while the ethylenepressure was kept at 40 barg. Thorough mixing was ensured throughout bymixing speeds of 1100 RPM's using a gas entraining stirrer. The reactionwas terminated after 30 minutes by discontinuing the ethylene feed tothe reactor and cooling the reactor to below 10° C. After releasing theexcess ethylene from the autoclave, nonane or heptane was added as aninternal standard for the analysis of the liquid phase by GC-FID. Theliquid contained in the autoclave was quenched with ethanol followed by10% hydrochloric acid in water. A small sample of the organic layer wasdried over anhydrous sodium sulfate and then analysed by GC-FID andGC-MS. The remainder of the organic layer was filtered to isolate thesolid polymeric products. These solid products were dried overnight inan oven at 100° C. and then weighed to yield 0.47 g of dry polymer. TheGC analyses indicated that the reaction mixture contained 46.85 goligomers. The product distribution of this example is summarized inTable 2.

Example 7-19 Ethylene Trimerisation Reaction UsingCrCl₃(bis-(2-ethylsulfanyl-ethyl)-amine)/MAO

Examples 7 to 19 were carried out using the procedure of Example 6 abovewith variations in the reaction conditions, quantities ofCrCl₃(bis-(2-ethylsulfanyl-ethyl)-amine) and MAO employed and the typeof solvent used. The total volume of the reaction mixture at the startof each reaction was 100 ml throughout. The results obtained for theseexamples are summarized in Table 2.

Example 20 Ethylene Trimerisation Reaction UsingCrCl₃(bis-(2-decylsulfanyl-ethyl)-amine)/MAO

A 0.004 molar solution of CrCl₃(bis-(2-decylsulfanyl-ethyl)-amine) intoluene (6 ml, 0.024 mmol) was transferred to a 300 ml pressure reactor(autoclave) containing a mixture of toluene (94 ml) and a MAO(methylaluminoxane, 1.12 mmol) at 80° C. The pressure reactor wascharged with ethylene after which the reactor temperature was maintainedat 90° C., while the ethylene pressure was kept at 30 barg. Thoroughmixing was ensured throughout by mixing speeds of 1100 RPM using a gasentraining stirrer. The reaction was terminated after 30 minutes bydiscontinuing the ethylene feed to the reactor and cooling the reactorto below 10° C. After releasing the excess ethylene from the autoclave,nonane or heptane was added as an internal standard for the analysis ofthe liquid phase by GC-FID. The liquid contained in the autoclave wasquenched with ethanol followed by 10% hydrochloric acid in water. Asmall sample of the organic layer was dried over anhydrous sodiumsulfate and then analysed by GC-FID. The remainder of the organic layerwas filtered to isolate the solid polymeric products. These solidproducts were dried overnight in an oven at 100° C. and then weighed toyield 0.09 g of dry polymer. The GC analyses indicated that the reactionmixture contained 43.90 g oligomers. The product distribution of thisexample is summarized in Table 3.

Example 21-27 Ethylene Trimerisation Reaction UsingCrCl₃(bis-(2-decylsulfanyl-ethyl)-amine)/MAO

Examples 21 to 27 were carried out using the procedure of Example 6above with variations in the reaction conditions and the quantities ofCrCl₃(bis-(2-ethylsulfanyl-ethyl)-amine) and MAO employed. The totalvolume of the reaction mixture at the start of each reaction was 100 mlthroughout. The results obtained for these examples are summarized inTable 3.

Example 28 Preparation of MAO on Alumina

Alumina (obtained from Sasol Chemie Gmbh as Puralox SBa200) was calcinedfor 3 hours at 550° C. under a nitrogen flow. The calcined alumina (4.80g) was suspended in toluene (20 ml). MAO/toluene solution (1.068M, 14.53mmol, 13.6 ml) was added slowly via a syringe to this alumina/tolueneslurry and the resulting mixture was stirred for 2 hours at roomtemperature. The supernatant solvent was finally taken off with asyringe.

Ethylene trimerisation Reaction usingCrCl₃(bis-(2-decylsulfanyl-ethyl)-amine)/alumina Supported MAO

A 0.001097 molar solution of CrCl₃(bis-(2-decylsulfanyl-ethyl)-amine) intoluene (21.88 ml, 0.024 mmol) was added to the alumina supported MAO(14.53 mmol on 4.80 g support). The resulting suspension was stirred atroom temperature for 5 minutes whereafter it was transferred to a 300 mlpressure reactor (autoclave) containing toluene (78.1 ml) at 75° C. Thepressure reactor was charged with ethylene after which the reactortemperature was maintained at 90° C., while the ethylene pressure waskept at 30 barg. Thorough mixing was ensured throughout by mixing speedsof 1100 RPM using a gas entraining stirrer. The reaction was terminatedafter 30 minutes by discontinuing the ethylene feed to the reactor andcooling the reactor to below 10° C. After releasing the excess ethylenefrom the autoclave, nonane or heptane was added as an internal standardfor the analysis of the liquid phase by GC-FID. The two phases of thereaction mixture were separated and the liquid phase was analyseddirectly by GC-FID. The solid particles in the reaction mixture wasfirst exposed to air before being dried overnight in an oven at 100° C.and then weighed. The mass of the dried solids was 5.48 g, indicatingthe formation of 0.65 g polymer during the reaction. The GC analysesindicated that the reaction mixture contained 40.99 g oligomers, ofwhich 0.4 mass % were butene isomers, 97.7 mass % were hexene isomers(99.6% being 1-hexene), 0.3 mass % were octene isomers and 0.5 mass %were decene isomers and heavier products.

Example 29 Ethylene Trimerisation Reaction UsingCrCl₃(bis-(2-ethylsulfanyl-ethyl)-amine)/MAO or Used MAO

A 300 ml pressure vessel was connected to a vacuum pump via a stainlesssteel tube with two glass cold traps, a pressure gauge and a needlevalve (to seal the reactor off) between the vacuum pump and the reactor.

The following five steps were followed:

-   1) CrCl₃(bis-(2-ethylsulfanyl-ethyl)-amine) (0.01055 g, 0.03 mmol)    was combined with 20 ml toluene in a Schlenk vessel and stirred for    5 minutes at room temperature. The resulting suspension was then    transferred to the pressure reactor containing a mixture of toluene    (80 ml) and a MAO (methylaluminoxane, 9.0 mmol) at 85° C. The    pressure reactor was charged with ethylene after which the reactor    temperature was maintained at 90° C., while the ethylene pressure    was kept at 30 barg. Thorough mixing was ensured throughout by    mixing speeds of 1100 RPM using a gas entraining stirrer.-   2) After 30 minutes, the temperature was decreased to 20° C. and the    stirring rate to 300 rpm, whereafter the excess ethylene was    released slowly, taking care to introduce a nitrogen blanket into    the reactor once the pressure had dropped below 1 barg. Once fully    depressurized, the reactor was sealed off and the needle valve    leading to the cold traps and the vacuum pump was opened gradually    until the pressure inside the reactor had decreased to 100 millibar    under atmospheric pressure. At this point, the temperature of    reaction mixture was also increased to 90° C. and a distillate    formed which was collected in the cold traps. As soon as the    formation of the distillate ceased, the needle valve outlet to    vacuum system was closed and the contents of the reactor was placed    under a nitrogen blanket again. The estimated loss of toluene from    the reactor during this flash distillation step was 33 ml.-   3) New CrCl₃(bis-(2-ethylsulfanyl-ethyl)-amine) (0.01055 g, 0.03    mmol) was then added to the reactor as a suspension in toluene, but    in 33 ml toluene (instead of the initial 20 ml) to ensure that the    quantity of toluene in the reactor remains more or less constant at    100 ml. The pressure reactor was charged again with ethylene while    the reactor temperature was maintained at 90° C. and the ethylene    pressure kept at 30 barg. The mixing speed was also increased again    to 1100 RPM.-   4) Steps 2 and 3 were repeated another two times before moving onto    step 5.-   5) The reaction was terminated after 30 minutes by discontinuing the    ethylene feed to the reactor and cooling the reactor to below 10° C.    After releasing the excess ethylene from the autoclave, the contents    of the reactor was combined with the contents of the cold traps and    either nonane was added as an internal standard for the analysis of    the liquid phase by GC-FID. The liquid contained in the autoclave    was quenched with ethanol followed by 10% hydrochloric acid in    water. A small sample of the organic layer was dried over anhydrous    sodium sulfate and then analysed by GC-FID. The remainder of the    organic layer was filtered to isolate the solid polymeric products.    These solid products were dried overnight in an oven at 100° C. and    then weighed to yield 0.70 g of dry polymer. The GC analyses    indicated that liquid phase contained 161.64 g oligomers, of which    97.9 mass % were hexene isomers (99.5% being 1-hexene).

Example 30 Ethylene Trimerisation Reaction UsingCrCl₃(bis-(2-decylsulfanyl-ethyl)-amine)/EAO

A 0.004 molar solution of CrCl₃(bis-(2-decylsulfanyl-ethyl)-amine) intoluene (7.5 ml, 0.03 mmol) was transferred to a 300 ml pressure reactor(autoclave) containing a mixture of toluene (92.5 ml) and EAO(ethylaluminoxane, 30.0 mmol) at 80° C. The pressure reactor was chargedwith ethylene after which the reactor temperature was maintained at 90°C., while the ethylene pressure was kept at 30 barg. Thorough mixing wasensured throughout by mixing speeds of 1200 RPM using a gas entrainingstirrer. The reaction was terminated after 30 minutes by discontinuingthe ethylene feed to the reactor and cooling the reactor to below 10° C.After releasing the excess ethylene from the autoclave, nonane orheptane was added as an internal standard for the analysis of the liquidphase by GC-FID. The liquid contained in the autoclave was quenched withethanol followed by 10% hydrochloric acid in water. A small sample ofthe organic layer was dried over anhydrous sodium sulfate and thenanalysed by GC-FID. The remainder of the organic layer was filtered toisolate the solid polymeric products. These solid products were driedovernight in an oven at 100° C. and then weighed to yield 2.37 g of drypolymer. The GC analyses indicated that the reaction mixture contained9.52 g oligomers, of which 3.4 mass % were butene isomers, 85.5 mass %were hexene isomers (98.2% being 1-hexene), 0.8 mass % were octeneisomers and 10.1 mass % were decene isomers and heavier products.

Example 31 Ethylene Trimerisation Reaction UsingCrCl₃(bis-(2-decylsulfanyl-ethyl)-amine)/EAO/TMA

A 0.004 molar solution of CrCl₃(bis-(2-decylsulfanyl-ethyl)-amine) intoluene (7.5 ml, 0.03 mmol) was transferred to a 300 ml pressure reactor(autoclave) containing a mixture of toluene (92.5 ml), EAO(ethylaluminoxane, 30.0 mmol) and TMA (trimethylaluminium, 3.0 mmol) at80° C. The pressure reactor was charged with ethylene after which thereactor temperature was maintained at 90° C., while the ethylenepressure was kept at 30 barg. Thorough mixing was ensured throughout bymixing speeds of 1200 RPM using a gas entraining stirrer. The reactionwas terminated after 30 minutes by discontinuing the ethylene feed tothe reactor and cooling the reactor to below 10° C. After releasing theexcess ethylene from the autoclave, nonane or heptane was added as aninternal standard for the analysis of the liquid phase by GC-FID. Theliquid contained in the autoclave was quenched with ethanol followed by10% hydrochloric acid in water. A small sample of the organic layer wasdried over anhydrous sodium sulfate and then analysed by GC-FID. Theremainder of the organic layer was filtered to isolate the solidpolymeric products. These solid products were dried overnight in an ovenat 100° C. and then weighed to yield 0.20 g of dry polymer. The GCanalyses indicated that the reaction mixture contained 23.90 goligomers, of which 1.5 mass % were butene isomers, 96.1 mass % werehexene isomers (98.9% being 1-hexene), 0.6 mass % were octene isomersand 1.7 mass % were decene isomers and heavier products.

Example 32 Ethylene Trimerisation Reaction UsingCrCl₃(bis-(2-decylsulfanyl-ethyl)-amine)/EAO/MAO

A 0.004 molar solution of CrCl₃(bis-(2-decylsulfanyl-ethyl)-amine) intoluene (7.5 ml, 0.03 mmol) was transferred to a 300 ml pressure reactor(autoclave) containing a mixture of toluene (92.5 ml), EAO(ethylaluminoxane, 8.55 mmol) and MAO (methylaluminoxane, 0.45 mmol) at80° C. The pressure reactor was charged with ethylene after which thereactor temperature was maintained at 90° C., while the ethylenepressure was kept at 30 barg. Thorough mixing was ensured throughout bymixing speeds of 1200 RPM using a gas entraining stirrer. The reactionwas terminated after 30 minutes by discontinuing the ethylene feed tothe reactor and cooling the reactor to below 10° C. After releasing theexcess ethylene from the autoclave, nonane or heptane was added as aninternal standard for the analysis of the liquid phase by GC-FID. Theliquid contained in the autoclave was quenched with ethanol followed by10% hydrochloric acid in water. A small sample of the organic layer wasdried over anhydrous sodium sulfate and then analysed by GC-FID. Theremainder of the organic layer was filtered to isolate the solidpolymeric products. These solid products were dried overnight in an ovenat 100° C. and then weighed to yield 0.95 g of dry polymer. The GCanalyses indicated that the reaction mixture contained 53.66 goligomers, of which 0.2 mass % were butene isomers, 96.6 mass % werehexene isomers (99.5% being 1-hexene), 0.4 mass % were octene isomersand 2.7 mass % were decene isomers and heavier products.

Example 33 Ethylene Trimerisation Reaction UsingCrCl₃(bis-(2-methylsulfanyl-ethyl)-amine)/MAO

The reaction was conducted in a 75 mL stainless steel autoclave equippedwith an addition funnel, gas inlet valve and a magnetic stirrer bar. Theaddition funnel was charged with 0.0039 g (0.012 mmol) ofCrCl₃(bis-(2-methylsulfanyl-ethyl)-amine) dissolved in 20 mL of tolueneand to the base of the autoclave was added 4.8 mL of 1.5M MAO solutionin toluene. Over 20 minutes the base of the autoclave was heated to 80°C., after which time the reactor was charged with ethylene to a pressureof 40 bar and the addition funnel was opened such that the Cr complexsolution was allowed to mix with the MAO solution. After 30 minutes at aconstant ethylene pressure of 40 bar the reaction was stopped by coolingthe autoclave to 0° C. and releasing excess ethylene. The gas releasedwas collected and analysed by GC. The liquid contained in the autoclavewas quenched with ethanol followed by 10% hydrochloric acid, and nonanewas added as a GC internal standard. The liquid/internal standardmixture was also analysed by GC. Both GC analyses indicated that 12.9546g oligomers were formed of which 12.1773 g (94 mass %) were hexeneisomers (99.7% being 1-hexene). Filtration of the liquids gave 0.0143 gof polyethylene.

Example 34 Ethylene Trimerisation Reaction UsingCrCl₃((2-ethylsulfanyl-ethyl)(3-ethylsulfanyl-propyl)-amine)/MAO

The reaction was conducted in a 75 mL stainless steel autoclave equippedwith an addition funnel, gas inlet valve and a magnetic stirrer bar. Theaddition funnel was charged with 0.0039 g (0.0107 mmol) ofCrCl₃((2-ethylsulfanyl-ethyl)(3-ethylsulfanyl-propyl)-amine) dissolvedin 20 mL of toluene and to the base of the autoclave was added 4.3 mL of1.5M MAO solution in toluene. Over 20 minutes the base of the autoclavewas heated to 80° C., after which time the reactor was charged withethylene. to a pressure of 40 bar and the addition funnel was openedsuch that the Cr complex solution was allowed to mix with the MAOsolution. After 30 minutes at a constant ethylene pressure of 40 bar thereaction was stopped by cooling the autoclave to 0° C. and releasingexcess ethylene. The gas released was collected and analysed by GC. Theliquid contained in the autoclave was quenched with ethanol followed by10% hydrochloric acid, and nonane was added as a GC internal standard.The liquid/internal standard mixture was also analysed by GC. Both GCanalyses indicated that 4.0487 g oligomers were formed of which 3.2795 g(81 mass %) were hexene isomers (97.9% being 1-hexene). Filtration ofthe liquids gave 0.0600 g of polyethylene.

TABLE 2 Ethylene trimerisation reactions usingCrCl₃(bis-(2-ethylsulfanyl-ethyl)-amine)/MAO CrCl₃ Activity Total LiquidProduct Distribution 1-Hexene complex Cr MAO Temp Pressure (g prod/Product Solids Liquids (Wt %) in C₆ Example (mg) (mmol) (mmol) (° C.)(barg) g Cr) (g) (Wt %) (Wt %) C₄ C₆ C₈ C₁₀+ (Wt %)  6 15.5 0.044 29.9100 40 21767 49.80 0.58 99.00 0.3 96.0 0.5 2.5 99.4  7 15.5 0.044 29.940 40 2750 6.29 13.40 86.60 0.2 91.8 2.5 2.3 99.8  8 15.5 0.044 29.9 14040 1700 3.89 19.40 80.60 0.8 94.1 0.8 1.3 99.3   9¹ 15.5 0.044 29.9 9040 6580 15.05 7.90 92.10 0.8 95.2 1.0 1.5 99.3 10 15.5 0.044 29.9 100 104424 10.12 2.49 97.51 0.8 94.2 0.7 2.8 98.6 11 15.5 0.044 29.9 100 5023954 54.80 1.78 98.22 0.5 94.8 0.8 2.9 99.4 12 3.9 0.011 7.5 100 4040503 23.17 0.60 99.40 0.1 98.5 0.4 0.7 99.6 13 15.5 0.044 9.0 100 4011500 26.31 3.07 96.93 0.1 99.2 0.4 0.5 99.5 14 10.6 0.030 9.0 90 3032459 50.63 0.03 99.97 0.2 96.2 0.5 2.9 99.5 15 4.2 0.012 3.6 90 3044242 27.60 0.30 99.70 0.1 97.7 0.4 1.6 99.6 16 10.6 0.030 3.6 90 3018116 28.26 0.76 99.24 0.1 97.8 0.4 1.5 99.6 17 1.4 0.004 1.1 85 3096251 20.02 0.16 99.84 0.1 98.5 0.5 0.8 99.7 18 4.2 0.012 2.4 85 5059312 37.01 0.10 99.90 0.1 98.0 0.7 1.1 99.7 19 10.6 0.030 3.6 85 1523784 37.10 0.18 99.82 0.1 95.5 0.3 3.9 99.4 ¹Cyclohexane was used asthe solvent in this reaction

TABLE 3 Ethylene trimerisation reactions usingCrCl₃(bis-(2-decylsulfanyl-ethyl)-amine)/MAO CrCl₃ Activity Total LiquidProduct Distribution 1-Hexene complex Cr MAO Temp Pressure (g prod/Product Solids Liquids (Wt %) in C₆ Example (mg) (mmol) (mmol) (° C.)(barg) g Cr) (g) (Wt %) (Wt %) C₄ C₆ C₈ C₁₀+ (Wt %) 20 13.8 0.024 14.4090 30 35250 43.99 0.21 99.79 0.4 97.5 0.4 1.3 99.4 21 15.0 0.026 2.60 9030 38796 52.45 0.30 99.70 0.1 96.7 0.4 2.8 99.5 22 15.0 0.026 1.30 90 4520327 27.48 2.44 97.56 0.4 94.6 0.6 3.8 99.7 23 6.9 0.012 1.20 100 4571018 44.31 0.30 99.70 0.2 97.5 0.6 1.5 99.7 24 6.9 0.012 0.60 90 4731700 19.78 1.05 98.95 0.2 96.6 0.5 1.4 99.7 25 4.6 0.008 0.40 90 4544000 18.30 0.67 99.33 0.1 98.7 0.8 0.4 99.7 26 6.9 0.012 0.36 90 4546350 28.92 2.37 97.63 0.1 98.4 0.6 0.9 99.7 27 6.9 0.012 0.36 90 4537650 23.49 0.49 99.51 0.1 97.9 0.6 1.3 99.7

1. A process for the oligomerisation of olefins, the process comprising the step of contacting the olefins at pressures from atmospheric to 100 barg and at temperatures of from 0° C. to 200° C., with a catalyst system, which comprises a mixed heteroatomic ligand, which ligand includes at least three heteroatoms of which at least one is sulfur and at least 2 heteroatoms are not the same, and a chromium.
 2. A process as claimed in claim 1, wherein the olefins are contacted with the catalyst system at pressures from 30 to 50 barg and at temperatures of from 80° C. to 100° C.
 3. A process as claimed in claim 2, wherein the catalyst is dissolved in an inert solvent.
 4. A process as claimed in claim 1, the system further comprising the step of generating the multidentate mixed heteroatomic complex of a chromium salt in-situ in a reaction mixture.
 5. The process of claim 1, wherein the catalyst system comprises a multidentate mixed heteroatomic ligand, which includes at least three heteroatoms of which at least one is a sulfur atom, and a chromium.
 6. The process of claim 5, wherein the ligand contains, in addition to sulfur, at least one nitrogen or phosphorous heteroatom.
 7. The process of claim 1, wherein none of the non-carbon based heteroatoms in the ligand is directly bonded to any of the other non-carbon based heteroatoms.
 8. A process for the oligomerisation of olefins, the process comprising a step of contacting the olefins, at pressures from atmospheric to 100 barg and at temperatures of from 0° C. to 200° C., with a catalyst system including a mixed heteroatomic ligand, which ligand having a chromium and at least three heteroatoms of which at least one is sulfur and at least 2 heteroatoms are not the same, wherein none of the heteroatoms in the ligand is directly bonded to any of the other heteroatoms, and the ligand is selected from the following ligand types: (a) R¹A(R²BR³)(R⁴CR⁵) wherein R¹, R³ and R⁵ may be hydrogen or be independently selected from the groups consisting of alkyl, aryl, aryloxy, halogen, nitro, alkoxycarbonyl, carbonyloxy, alkoxy, aminocarbonyl, carbonylamino, dialkylamino, or derivatives thereof, or aryl substituted with any of these substituents; R² and R⁴ may be the same or different and are C₁ to C₁₅ hydrocarbyls; A is nitrogen or phosphorous; and B and C are sulfur; and (b) R¹A(R²BR³R⁴)(R⁵CR⁶) wherein R¹, R³, R⁴, and R6 may be hydrogen or independently be selected from the groups consisting of alkyl, aryl, aryloxy, halogen, nitro, alkoxycarbonyl, carbonyloxy, alkoxy, aminocarbonyl, carbonylamino, dialkylamino, or derivatives thereof, or aryl substituted with any of these substituents; R² and R⁵ may be the same or different and are C₁ to about C₁₅ hydrocarbyls; A and B are independently nitrogen or phosphorous; and C is sulfur; and (c) A(R¹BR²R³)(R⁴CR⁵) wherein R², R³, and R⁵ may be hydrogen or independently be selected from the groups consisting of alkyl, aryl, aryloxy, halogen, nitro, alkoxycarbonyl, carbonyloxy, alkoxy, aminocarbonyl, carbonylamino, dialkylamino, or derivatives thereof, or aryl substituted with any of these substituents; R¹ and R⁴ may be the same or different and are C₁ to about C₁₅ hydrocarbyls; B is nitrogen or phosphorous; and A and C are sulfur; and (d) A(R¹BR²R³)(R⁴CR⁵R⁶) wherein R², R³, R⁵ and R6 may be hydrogen or independently be selected from the groups consisting of alkyl, aryl, aryloxy, halogen, nitro, alkoxycarbonyl, carbonyloxy, alkoxy, aminocarbonyl, carbonylamino, dialkylamino, or derivatives thereof, or aryl substituted with any of these substituents; R¹and R⁴ may be the same or different and are C₁ to about C₁₅ hydrocarbyls; B and C are independently nitrogen or phosphorous; and A is sulfur. 